A vehicle transportation system may include routes over which vehicles travel. These routes may cross routes of other transportation systems, such as where rail tracks and road or highway systems cross over each other. To warn the vehicles, crossing gates may be provided at locations where the routes intersect, with the crossing gates configured to warn operators of the vehicles and inhibit (e.g., prevent) vehicles from crossing a route while another vehicle is traveling on the route at or near the crossing.
Some known railroad crossings use a warning predictor track circuit that detects motion of a rail vehicle toward the crossing. Warning predictors (also referred to as crossing predictors) may calculate the time of arrival of the rail vehicle to the crossing based on the motion that is detected. The warning predictors activate crossing warning devices (e.g., lights, gates, bells, speakers, or the like) a specified (e.g., designated) amount of time prior to arrival of the rail vehicle at the crossing. The designated amount of time may be set by a government regulation, by the operator or owner of the rail vehicle or crossing, or another entity. Optionally, the designated amount of time may be set to exceed such a regulation or time that is set by the operator, owner, or other entity. Crossing predictors are commonly used where there are mixed rail vehicle types (freight, passenger, or the like) traveling along the routes, and/or where speeds of the rail vehicles may vary dramatically.
In some systems, for example rail systems that use catenaries or third rails to provide energy to rail vehicles, electrical interference may be too high for predictor systems to function accurately. Thus, in some applications, crossing gates or lights may be activated based on occupancy of the route by a rail vehicle within a given distance of a crossing, without respect to relative speed or arrival time of the rail vehicle at the crossing. If track circuits that simply activate the crossing based on occupancy of the route are used (as opposed to detecting motion of the rail vehicle), the warning times provided at the crossing can vary significantly depending upon the speed of approach of the rail vehicle. Long warning times can be undesirable because of the unnecessary delay caused to operators of other vehicles trying to move through the crossing. Overly long warning times may tempt impatient operators of such vehicles to move the vehicles around the crossing gates and/or disregard audible or visible warnings if the operators do not see any rail vehicles imminently approaching after some period of time.
Traditional predictor circuits are limited by practical considerations to a range extending a given distance from a crossing. Thus, vehicles may travel at a speed that exceeds the ability of the predictor circuit to detect presence of the vehicle in time to lower a gate within a desired or designated time range. Some systems account for such speeds exceeding the ability of the predictor circuit by sending a message from the approaching vehicle when traveling at such faster speeds before encountering the effective range of the predictor circuit. The term “approaching vehicle” refers to the vehicle that is traveling toward the crossing and for which the warning system is to be activated to warn operators of other vehicles at the crossing and/or prevent these other vehicles from traveling through the crossing until the approaching vehicle completes passage through the crossing. The effective range of the predictor circuit represents the distance or locations in which the predictor circuit is able to identify the presence of a vehicle traveling toward the crossing. The message that is sent by the vehicle to the predictor circuit can communicate a relative time (e.g., time from when the message was sent) that represents when the vehicle is expected to arrive at the crossing. For example, the message may indicate that the approaching vehicle expects to arrive at the crossing in one minute from the time that the message was sent by the vehicle. Delays in sending, receiving, and/or processing the message using relative time may result in initiation of closing the crossing or otherwise warning other vehicles at the crossing at a time exceeding a desired time for closing, in order to account for worst case delays, which may be around ten seconds or more. In such systems, crossings will frequently activate earlier than desired, resulting in overly long waiting periods, and resulting in inconsistent wait times for operators of vehicles waiting at the crossing. Such systems also fail to address issues resulting from relatively slower speeds of the vehicle that is approaching the crossing.
In some known warning systems, equipment disposed onboard an approaching vehicle is able to activate warning systems at crossings that are controlled by wayside units disposed at or near the crossings. The onboard equipment sends a single message to the wayside unit when the approaching vehicle is traveling toward the crossing. This single message indicates a relative time of when the approaching vehicle expects to reach the crossing. For example, the single message may indicate that the approaching vehicle expects to arrive at the crossing in forty-five seconds. In response, the wayside unit activates the crossing by counting down the received time (e.g., counts down from forty-five seconds) to a designated (e.g., minimum or other) warning time. When the countdown of the wayside unit reaches the designated warning time, the wayside unit activates the warning system at the crossing.
These known warning systems are not without drawbacks. Because only a single message is communicated from the onboard system to the wayside unit, this single message may not be received and/or may be degraded or interfered with due to various problems with communication and/or external interferences with communication. Additionally, these systems communicate the message with a built-in buffer time period to allow for changes in the speed of the approaching vehicle and/or to account for delays in communicating with the wayside units. For example, the relative time communicated by the message may include both the time period that the approaching vehicle expects to use to travel to the crossing and an additional buffer time period that allows the approaching vehicle to accelerate during travel toward the crossing while still activating the warning system before the vehicle arrives at the crossing. Because of this additional, built-in buffer time period, the warning system may activate too soon and other vehicles at the crossing may be warned of the approaching vehicle too soon. As described above, impatient operators of these other vehicles may attempt to circumvent such a warning system by attempting to drive through the crossing ahead of the approaching vehicle.